Target structure for barrier grid storage tube



2 Sheets-Sheet l1 INVENTORS RALPH DELA/v0 JR.

A65/VT R. B. DELANO, JR., ETAL TARGET STRUCTURE FOR BARRIER GRID STORAGE TUBE Jan. 7, 1958 Filed April 2s, 1954 Jan. 7, 1958 I Yfla. B DE LANo, JR., ETAL 3l-9,4m

' TARGET sTRUc Filed April 2s, 1954 TARGET STRUCTURE FOR BARRIER GRID STORAGE TUBE Ralph B. De Lano, Jr., and .lohn B. Little, Poughkeepsie, and Frederick L. Stutz, Pleasant Valley, N. Y., assignors to International Business Machines Corporation, New York, N. Y., a corporation of New York Application April 23, 1954, Serial No. 425,072 15 Claims. (Cl. 313-68) This invention relates to electron discharge devices and n particular to improvements in memory tubes of the :athode ray type.

In an electrostatic storage tube, binary information is stored in the form of charges established on the surface )f a dielectric target by potentials applied to a capacitaively coupled backing plate while the beam impinges an :lemental target region. A tube of this type is disclosed n the application of A. Salecker, tiled February 18, 1953, erial No. 337,544, now U. S. Patent No. 2,795,840, granted .lune 18, 1957.

ln establishing distinguishable charge states on the :arget surface, the cathode beam is directed to an elenental region and secondary electrons emitted therefrom end to be attracted to a collector electrode placed near he target end of the tube. The bombarded region tends o attain an effective potential related to that of the colector electrode and the .charge thereon is determined by nodulation of potential applied to the backing plate. With the backing plate held negative at the time the :athode beam is turned oit, the bombarded region be- :ornes positive with respect to the effective collector poential, Whereas, if the backing plate is not modulated or t modulating pulse terminated before the beam is turned rif, the elemental region remains at an equilibrium poential with respect to the effective collector voltage.

In the storage tube described in the above mentioned application, a ne barrier grid electrode is placed on or :iear the dielectric surface to shield one elemental stortge region from another and reduce the redistribution of =econdary electrons. This effect occurs during bombardnent of an elemental region in a tube used in the con- /entional Williams type system when some of the emitted Iecondary electrons form a space charge and tend to rain ack on the target surface rather than migrate to the rollector. Since some of the target regions may retain :harges positive with respect to the collector, there is a Aendency for these secondary electrons to redistribute hemselves and neutralize the adjacent established charge tates in unbonibarded regions, however, this action is `,lso considered related to the initial velocity of the secndary electrons.

To minimize this redistribution effect the barrier grid s placed in direct contact with the target surface in the tructure set forth in the above mentioned application 1nd the effective collector potential is established at a alue between that applied to these two electrodes.

'in determining which one of the 'two charge states is :stablished in a particular region, the spot on the target is )ombarded and an output signal is detected at the backing ilate. lt has been found that a spurious voltage also tppears at the backing plate during this interval and also turing the interval that the beam is turned olf. This voltige increases the noise level or the degree of voltage dif- :erence obtained in determining which of the two charge ttates had been previously established.

Accordingly, it is an object of the present invention to vorovide an improved target structure for a barrier grid @,Slgflllg Patented Jan. 7, 1958 memory tube whereby the signal to noise level ratio is increased and the ability to distinguish between representative charge states is improved.

Another object of this invention is to provide au improved means for uniformly positioning the barrier grid with respect to the dielectric target surface in reducing the effects of electron redistribution.

Still another object of this invention is to provide an improved charge storage surface for a dielectric target.

A `further object of the invention is to provide a virtual spacing between the barrier-grid electrode and the target surface in increasing the signal to noise level ratio.

Other objects will be pointed out in the following description and claims and illustrated in the accompanying drawings which disclose, byway of example, the principle of the invention and a contemplated mode of applying the principle.

In the drawings:

Figure 1 illustrates a storage tube of the barrier grid type.

Figure 2 is a View of the target structure for the tube shown in Figure 1, showing the barrier grid and target subassembly in greater detail and at right angles to the other ligure.

Figures 3 and 4 are plan views of the barrier and collector grid subassemblies.

Referring to Figure 1, the memory tube comprises an envelope 1 of glass or other suitable material within which is positioned an electron gun Z for forming and focusing a cathode beam upon a target 3. The beam is produced by a thermionic cathode l and is turned on under control of an apertured control grid electrode 5'. An anode electrode 6 is positioned in alignment with the beam and accelerates the electrons emitted from the cathode Il. Elements 7, 8 and 9A are focus electrodes and element 9B is a shield electrode formed from aperturecl metal discs and spaced along the path of the beam. Pairs of vertical and horizontal deflection plates 10V and 10H respectively, direct the beam to particular elemental regions on the surface of the target 3, as determined by potentials applied thereon by conventional means for producing the desired type ot target scansioni. A collector electrode 1l is mounted in spaced relationship to a barrier grid comprising two layers of parallel wires 12A example by the evaporation of aluminum as in well known coating processes.

The target assembly comprises the collector and barrier electrodes, the dielectric target and the backing plate element mounted in a stainless steel frame member 14 as shown in greater detail in Figure 2. The grids 11 and 12A-i2l5 are supported on individual frame members 16 and 15, respectively, and are so positioned within the support 1d to be separated by a distance of approximately 0,010 inch. The members 1.5 and 16 are fabricated of a ceramic material having a coelicient of expansion comparable to that of the grid wires in order to allow equal contraction and expansion of the parts during outgassing and use. Other materials having comparable expansion characteristics may be used, however.

As described in detail in the aforementioned application, the collector grid comprises strands of tungsten wire 0.0006 inch in diameter spaced at turns per inch and the barrier grid comprises two layers of cross wound tungsten wires wound at 30G turns per inch. The collector wires are arranged at 4.5 angle to the barrier grid Wires as shown in Figures '5 and 4.

The target is formed of mica. and is held in contact with the frame, 15 bythe first layer of barrier grid wires?y 3 12A so that these gridwires are in direct contact with thel surface facing the electron gun. It has been found that in cutting vthe mica target into the desired shape and dimensions, theedges have minute v*irregularities and the surface maynot beprecisely flat so that vsome spacing exists between the barrier-,grid wires and portions of the target surface.Vv To eliminatethis problema spring member 17 is mountedwithin the frame member 15 so as to act against the. central4 targetarea'causingit to bexbowed out suiciently to hold'the wires in essentially intimate contact with the target .throughout their length.

`.The'spring member 17 is .positioned at right angles to thelayer of wires 12A directly on the target surface, as seenvin yFigure 2, and thus furthertends to maintain contact between individual ones of the first and secondlayers o f wires forming the barriergrid AAs mentioned;v above,-a-noisevoltage develops atthe backingplate terminal and-appears to -be caused by the pulseapplied to this electrode inthe writing cycle, however, other conditions within the tube are thought to contribute to its presence. It has been found, however, that thisl noisejvoltage `may be' essentially eliminated by application of a coating of powdered insulating material, such asxmagnesiumfoxide, on the bombarded target -surface. Other. insulating oxides such as aluminum oxide may also. be .used rather than magnesium', and in addition, insulating materials of the class of phosphors such as y magnesium tungstate and'zincsulphide have been found to provide an improved operationin this respect. With the use vofphosphormaterials,l the backing plate may be madefrom a-.transparent conductor applied to the surface ofthe .dielectric-target so that the' bombarded region may1be=visuallyf observed. A"A further method for treat` mentfofithe 'target surface and one considered to producetv evenv more.satisfactory-results consists of grinding or lapping the targetv surface -with an abrasive of one of the above mentioned powdered materials,` for lexample 'aluxnL` num:'.oxide..y '-1`hs1 rough'ens thev surface lof the' mica and'provides-a virtualspacing between the target and the adjacent :layer 'of grid wires v'equivalent to a 'fraction of a mill. In addition, s'om'eoffthe aluminum oxide particles used Yas the'iabrasive are pressed into the target surface in the' llapping operation'. The roughened vsurface or powdered insulating coating material is designated Aby thel label18 4as shownin Fg'u're'Z.

As a'resultof thetreatmentof the target surface. de-` scribedlandtliestructure' for obtaining uniform contact between the treated surface and the grid wires throughout thefsurface, the veffects of redistribution and the 'signal to noise 'level' in 'o'p'erationof the memory tube is greatlyl improved. "I

While there ,haverbeerr shown and described and pointed-out lthe"fundamental novel features of the invention' as yapplied to 'a preferred embodiment, it will be understood'that various.' omissions and substitutions and changesinthe form and details of the device illustrated and-in it'soperation'niaybe made by those skilled in the art -withoufdepart'ing from the spirit of theinvention.

Itfis Ythe intention, therefore, to be limited only as indicated lby the scope of 'thefollowing'claims A'1.A'cath'ode rayv tube comprising an envelope, means within said envelope lfor forriling an electron beam along a path, a' target"ele`ctr'ode` within said envelope mounted transverse to s aidbe'mpath, said target electrode including a sheet of dielectric material having a roughened surface `intercepting saidfb'eam path, a first electrode comprising'a `layer of' parallel wires in contact with said roughened surface, a second electrode positioned between saidrst electrode' and said. beam formir means,v and a backing plate electrode' in contact with the opposite surface of said dielectric sheet. 3

.2.--An electrostaticfmemory tube comprising an envelope,rmeans Within said 'envelope for forming ancl'direct- 4 ing an electron beam along a pathya `target electrode within said envelope mounted transverse to said beam path, said target electrode comprising a sheet of dielectric material 4having one surface coated with insulating metallic oxide particles, said surface being arranged to nterccpt said beam path, a backing plate electrode in contact with the opposite surface of saiddielectric'fsheet, a' barrier grid electrode comprisinga layer of parallel wires positioned in` contact v with said c oa te d surface,-v a collector electrode positionedtransverse to .said beam path and spaced from said.barrier.;,grid..electrodet 3. A target electrode fora cathode .rayf-typelstora'ge tube comprising a dielectric surface, a coating of insulating metallic oxide 'particles Vori said surface, abarrier electrode including a `first layer of parallel wires in contact with said coating and a further layer of parallel wires transverse to and in contact with said rst layer, a collector electrode including a" pluralitymofparallel wires arranged lto bisect the anglefformed betweenthe' rst and second layers of wires of said barrier electrode andspaced therefrom. 5i." 4. A target electrode` for'acathode'ry type"`storag`e` tube comprisinga sheet'ofdielectric lmaterial having af roughened surface for intercepting an' electron beam,l a.: barrier 'grid electrode including a first layer of parllel wires in contactwith said roughenedsurface anda ther layer ofparall-el wires 'arrangedtransverse to said first layer and in contact therewitin'a collector electrode including a plurality of parallel wires'arrangedtobiseet the angle formed between wiresof said'barrier grid and in a plane spaced from and parallel to said yfurther layer' 5. A cathode ray tube comprising an en velope,fm`eans f within said envelope for forming an electron beam alon'gff a path, a frame member, a target electrode within said" envelope mounted in said v'frame mem'ber transverse" to said beam path, said target electrode including asheetof dielectric material having `a roughenedfsurfaceintercept ing said beam p'ath,'a rst'gr'id electrode comprising''aE layer of parallel wires mountedon" said frame inernb'erfr in contact with said roughened surface, means 'r'ntiunted'- on the back of the target felectrod for bowing sai d'she -,tY o f dielectric material-so as to maintainintimate "contact between'said target and said layer of'wircs throughout their length, a backingplate electrode in contactwith"` the opposite surface of'said targetyandiasecond grid!y electrode positioned betweenjsaid first grid electrode and'f said beam forming means.v v Q 6. A target assembly for a lcathode ra'y typey s torag tube comprising'a dielectric 'charge storage surface,"a" coating of insulating metallic oxide on said surface a. barrier electrode including a first laye'fof parallel 'vs 'iresf` in contact with said coating anda furthela'yer ofwii'e'sf transverse to saidrst'la'yer, means mounted on thejbacl`r of the target' electrode for bowing said' target so as "to: maintain intimate contact' between said coated target sur-fl face and the Wires of'said first layer"thro`u'ghout their length, and a collector electrodeincludinga plurality of parallel wires in a plane spaced from said lsecondlayer'v ofwires. y .1

7. A cathode 'raytube comprising an envelope,l means within said yenvelope for forming' an electron beamalong,v a path, a frame member', a target yelectrode within saidky envelope mountedon said framemem'ber transverse to said beam path, said target electrode including a sheet o f mica having a roughened surface intercepting said be'am path, a irst electrode ycomprising allayerfof parallel mounted in said frame memb'erand in contact with said;l

and said roughened surface."`

8. In a cathode ray'typ'e storagetube,"altarg'etI elec! trode comprising ashe'et of dielectric material, a barrierelectrode comprising'aplurality of parallel 'wires m contact with one surface of said sheet, said surface being roughned to maintain a virtual spacing of less than one mil between said wires and surface. i

9. In a cathode ray type storage tube, a target electrode comprising a sheet of dielectric material having a roughened surface, a barrier electrode comprising a first layer of parallel wires in contact with the roughened surface of said sheet, a virtual spacing being maintained between said rst layer of wires and said surface, a second layer of wires transverse to' said rst layer land in contact therewith, means mounted on the 'back of the target electrode for maintaining contact between said second and rst layer of wiresand between said rst layer of wires and said roughened surface, a collector electrode comprising a layer of wires spaced from said second layer and arranged to bisect the angle formed between wires of said barrier grid and spaced therefrom, and `a backing plate electrode in contact with the opposite surface of said dielectric sheet.

10. A cathode ray tube comprising an envelope, means within said envelope for forming an electron beam along a path, a target electrode within said enveolpe mounted transverse to said beam path, said target electrode including a sheet of dielectric material having a phosphor coated surface intcrcepting said beam path, a rst electrode comprising a layer of parallel wires in contact with said coated surface, a second electrode positioned between said rst electrode and said beam forming means, and a transparent conductive backing plate electrode in contact with the opposite Surface of said dielectric sheet.

11. An electrostatic memory tube comprising an envelope, means within said envelope for forming and directing an electron beam along a path, a target electrode within said envelope mounted transverse to said beam path, said target electrode comprising a sheet of dielectric material having one surface coated with a phosphor material, said surface being arranged to intercept said beam path, a backing plate electrode in contact with the opposite surface of said dielectric sheet, a barrier grid electrode comprising a layer of Wires positioned in con tact with said coated surface, and a collector electrode positioned transverse to said beam path and spaced from said barrier grid electrode.

12. A target assembly for a cathode ray type storage tube comprising a dielectric target having a charge storage surface, a coating of powdered insulating material on said surface, a barrier electrode including a rst layer of parallel wires in contact with said coated surface and a further layer of wires transverse to said rst layer, means mounted on the back of the target electrode for bowing said target so as to maintain intimate contact between said coated target surface and the wires of said first layer throughout their length, and a collector electrode including a plurality of parallel wires in a plane spaced from said second layer of Wires.

13. A cathode ray tube comprising an envelope, means within said envelope for forming an electron beam along a path, a frame member, a target electrode within said envelope mounted on said frame member transverse to said beam path, said target 4electrode including a sheet of mica having a phosphor coated surface intercepting said beam path, a first electrode comprising a layer of parallel wires mounted in said frame member and in contact with' said coated surface, a spring member mounted on said frame and acting against the opposite surface of said target to maintain intimate contact between said wires and said coated surface.

14. In a cathode ray type storage tube, a target electrode comprising a sheet of dielectric material, a barrier electrode comprising a plurality of parallel wires in contact with one surface of said sheet, said one surface being coated with powdered insulating material to maintain a virtual spacing between said wires and surface.

15. In a cathode ray type storage tube, a target electrode comprising a sheet of dielectric material, a barrier electrode comprising a first layer of parallel wires in contact with one surface of said sheet, said sheet being coated with powdered insulating phosphor material to maintain a virtual spacing between said first layer of wires and said surface, a second layer of wires transverse to said rst layer and in contact therewith, means mounted on the back of the target electrode for maintaining contact between said second and rst layer of Wires and between said rst layer of wires and said coated surface, a collector electrode comprising a layer of wires spaced from said second layer and arranged to bisect the angle formed between wires of said barrier grid and spaced therefrom, and a transparent conductive backing plate electrode in contact with the opposite surface of said dielectric sheet.

Jensen Jan. 23, 1951 Rajchman July 22, 1952 

